# Einführung

Streams are the way of generalizing file, network, data compression, and other operations which share a common set of functions and uses. In its simplest definition, a `stream` is a resource object which exhibits streamable behavior. That is, it can be read from or written to in a linear fashion, and may be able to fseek() to an arbitrary location within the stream.

A `wrapper` is additional code which tells the stream how to handle specific protocols/encodings. For example, the `http` wrapper knows how to translate a URL into an `HTTP/1.0` request for a file on a remote server. There are many wrappers built into PHP by default (See Unterstützte Protokolle und Wrapper), and additional, custom wrappers may be added either within a PHP script using stream_wrapper_register(), or directly from an extension. Because any variety of wrapper may be added to PHP, there is no set limit on what can be done with them. To access the list of currently registered wrappers, use stream_get_wrappers().

A stream is referenced as: `scheme`://`target`

- `scheme` (string) - The name of the wrapper to be used. Examples include: file, http, https, ftp, ftps, compress.zlib, compress.bz2, and php. See Unterstützte Protokolle und Wrapper for a list of PHP built-in wrappers. If no wrapper is specified, the function default is used (typically `file`://).
- `target` - Depends on the wrapper used. For filesystem related streams this is typically a path and filename of the desired file. For network related streams this is typically a hostname, often with a path appended. Again, see Unterstützte Protokolle und Wrapper for a description of targets for built-in streams.

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